Latches

SN74LS259BD is a 8-bit addressable lattice which is widely used in various applications. The latch consists of 2 sets of inputs: Set Input (SI) and Reset Input (RI). The SI input is used to Set the latch to logic 1, whereas the RI input is used to Reset the latch to logic 0. In addition to these inputs, there is an inverted clock input (CLK\\') which is used to control the operation of the latch.

Application Field

The SN74LS259BD is widely used in many applications due to its wide voltage range, robust latch architecture and flexibility in applications. It can also be used to provide addressable latches with smaller size as compared to conventional latches. The applications of the SN74LS259BD includes memory address decoding, data bus latch, digital multiplexer, counter and timing circuits.

Working Principle

The operation of the SN74LS259BD can be understood with the help of the following diagram. When the clock enable signal clk is at logic 0 or low, the latches enable signal, LE, is at logic 0 or low. In this condition, the outputs of the latch are in a tri-state condition and neither Set nor Reset input can control the outputs. This condition is known as \'no-change state\' and is useful when the latch is being used for multiplexing data from various sources.

When the clk is at logic 1 (high) and LE is at logic 1, the latch is in a condition known as the \'setting\' or \'setting up\' state. At this instant, if the SI pin is at logic 1, the outputs of the latch are controlled by the SI, setting the outputs to logic 1. Similarly, when the RI pin is at logic 1, the outputs of the latch are controlled by the RI, resetting the outputs to logic 0.

The SN74LS259BD can be used with two conditions: pulse mode and level mode. In the pulse mode, the SI and RI signals must have a width longer than the clk pulse width. This guarantees that the latch is in the \'setting up\' state before the SI or RI signals are applied to the latch. In the level mode, the SI and RI signals must be held high for the entire duration of the clk pulse. This ensures that the latch is \'setting up\' for as long as the clk is high. The SN74LS259BD is designed to save power by using the active low enable (LE) which turns off all the unnecessary transistors when not in use.

The SN74LS259BD is commonly used in many applications and provides an efficient, robust and addressable latch architectures. It can be used in applications such as memory address decoding, data bus latch, digital multiplexer, counter and timing circuits. The versatility and reliability of the SN74LS259BD makes it a popular choice for applications requiring reliable addressable latches.